This invention relates to the building of pneumatic tires. More particularly it relates to a step in the construction of a belted radial ply pneumatic tire wherein three or more cord reinforced belts are positioned between a tire carcass and a tire tread, and wherein wedges of uncured rubber are applied along the edges of at least one of the intermediate belts to reduce ply separation between the edges of adjacent belts.
The construction of a radial ply tire involves the fabrication of a tire carcass with bead rings and sidewalls on a cylindrical drum followed by forming the carcass into toroidal shape. One or more reinforced belts are wrapped sequentially around the outer circumference of the carcass after which a tread is applied to the carcass on top of the reinforced belt or belts. The xe2x80x98greenxe2x80x99 or uncured tire is then transferred to a tire mold where it is formed under pressure into a final shape and then cured or vulcanized.
Each reinforced belt is made from a plurality of closely spaced cords embedded in uncured rubber, the cords extending at an angle of about 18xc2x0 to 26xc2x0 with respect to the equatorial plane of the tire. When two belts are used, the cord angles are equal but aligned in opposite directions with respect to the equatorial plane. Inasmuch as the cords are not parallel to the equatorial plane, the ends of the cords are exposed along the edges of the belts. The cords used in belts may comprise nylon, polyester, rayon, cotton, aramid or steel.
The exposed cord ends along the edges of the belts create discontinuities which can potentially cause problems such as ply separations, air entrapment and other irregularities in a finished tire. The previously mentioned potential problems are more likely to occur when steel cords are used for the belt reinforcement. Conventionally, a good adhesive bond between rubber and steel is achieved by plating the steel with brass, the latter forming a secure bond with the rubber. Problems arise, however, when the cut ends of the steel cords terminate along the edge of the belt because these ends are not plated. Thus, separation between the rubber and the ends of the steel cord is more likely to occur, thereby giving rise to one or more of the aforementioned problems.
In the construction of light and intermediate-duty tires, such as truck tires, three or four belts may be placed between the tire carcass and the tread. When a tire having three or four belts rolls along the ground, the cord angle in each belt has a tendency to change as the belt moves through the tire footprint (the contact area between the tire tread of the moving tire and the surface on which it is rolling). The cord shift is most pronounced in the middle belt or belts. Thus, when three belts are used in the tire construction, the shift is noted mostly between the 1st and 2nd belt. When four belts are used, the change in cord angle is most pronounced between the 2nd and 3rd belts because the latter adjacent belts have cords at opposite angles. This shift in cord angle can cause the reinforcing cords in the belt to pull loose from the rubber in which the cords are encapsulated.
One solution to these potential problems is to embed each edge of the middle or intermediate belt or belts in a wedge-shaped strip of uncured rubber. The rubber wedge is typically prepared by extrusion of a continuous length of uncured rubber at a location remote from the tire building operation. The extruded rubber wedge is cooled and rolled onto a storage spool with an intermediate plastic sheet serving as a barrier between adjacent folds of the wedge. The diameter of the storage spool is substantially less than the outer diameter of the tire carcass around which the wedge is eventually wrapped. The wedge is later unrolled and two strips of the wedge are applied separately to the edges of a belt to embed the exposed cord ends. This additional manufacturing step adds to the labor and expense of building a pneumatic tire.
The rolled wedge on the storage spool begins to age or cure in storage and thereby decreases its ability to bond to and encapsulate the edges of the belts. Furthermore, the wedge begins to degrade as it develops wrinkles, internal stresses, folds and deformation while stored on the spool. Due to the relatively small size of the wedge, it does not lend itself to being hauled with automatic pick-up and application equipment. Also, the tail end of the wedge must be re-aligned on the belt and manually spliced to the front end of the wedge during application. Furthermore, the wedge being stretched and compressed during application to the belt, creates a non-uniform gage or spacing between the edges of one belt and the next adjacent belt above or below it, thereby contributing to non-uniformities within the tire.
The direct extrusion of a cushion gum strip on to a rotating tire carcass in retreading operations has previously been described in various prior art patent such as U.S. Pat. No. 5,162,070 and U.S. Pat. No. 5,458,727.
The placement of uncured, wedge-shaped strips directly to a tire carcass during the fabrication of a new tire is shown in U.S. Pat. No. 4,283,241. The wedge strips are associated with the formation of the sidewalls of the tire and are not used to embed the ends of the belts beneath the tire tread.
U.S. Pat. No. 2,649,134 describes the application of a protective neoprene cover over the sidewall of a tire, preferably by calendering a thin layer of neoprene stock in heated condition on to the sidewall and firmly pressing them together.
None of these prior art references are directed at the aforementioned problems associated with the use of wedge strips along the edges of the belts in new tire construction.
It is an object of the present invention to provide a method for making a belt assembly from a cord reinforced belt and wedges of uncured rubber for use in the construction of pneumatic tires as defined in one or more of the appended claims and as such having the capability of accomplishing one or more of the following subsidiary objects.
Another object of the present invention is to provide a method for improving the uniformity and repeatability of producing light to intermediate duty truck tires; Yet another object of the present invention is to improve the rate of manufacture of reinforced belt assemblies for pneumatic tires, while at the same time reducing the labor time and expense of this procedure.
Still another object of the present invention is to provide a technique for decreasing the rate of failure along the side edges of the intermediate belt or belts in light and intermediate duty truck tires.
These and other objects which will become readily apparent from the following description are achieved in the manner to be hereinafter described.
The present invention relates to a method for constructing a cord reinforced belt assembly used in the construction of a pneumatic tire, comprising the steps of extruding at least one, and preferably two wedges of uncured rubber, preferably gum rubber; depositing one wedge of uncured rubber along each side edge of a length of belt reinforced with cords of metal such as brass plated steel, or of fibers of nylon, rayon, cotton, aramid or polyester; roll forming the wedges of rubber along the side edges of the reinforced belt material to embed each side edge in rubber wedge, and cutting the belt and the wedges to form a belt assembly having two ends. The wedges are extruded and then roll formed on to the edges of the belt at a temperature of between 77xc2x0 C. and 115xc2x0 C. The reinforcing cords in the belt material form an angle of between 18xc2x0 and 26xc2x0, and preferably between 21xc2x0 and 23xc2x0 with respect to the equatorial plane of the tire. The tire preferably has a belt assembly that contains three or four reinforced belts with one of the intermediate belt or belts roll formed with the wedges of the invention. In a tire having four reinforced belts, the cords in the second belt are disposed at a cord angle which is equal and opposite to the cord angle in the third belt, with respect to the equatorial plane of the tire and the wedges are provided between the second and third belt.
Another aspect of the invention relates to a method for applying at least four reinforcing belts onto a toroidal tire carcass. The method comprises the steps of; extruding a pair of uncured elastomeric wedges; depositing one of the elastomeric wedges along each side edge of a length of cord reinforced belt material; roll forming the elastomeric wedges and side edges to embed each side edge of the belt into one of the wedges; cutting the belt to a length equal to the circumference of the carcass; and wrapping the belt with the elastomeric wedges around the carcass so that the wedges are between the second and third belts. The wedges are extruded and roll formed at a temperature in the range or between 77xc2x0 C. and 115xc2x0 C. and at pressures of between 1400 and 2200 psi (9653 and 15170 kPa). The belts preferably are reinforced with steel cords, typically plated with brass or with cords of a suitable natural or synthetic material such as nylon, polyester, cotton, rayon or aramid.
Other objects, features and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed description.